The use of completely blocked polyisocyanates for the crosslinking of cationic binders, including those binders which are used in cathodically depositable paints are known, for example in U.S. Pat. No. 2,995,531; DE-AS 20 57 799, and U.S. Pat. No. 3,799,854. In mixtures of low molecular weight resin components, particularly in electrodeposition systems, disproportionation of the paint material occurs.
To overcome the separation problem, a large number of binders have been developed wherein the introduction of protonizable groups is carried out by amine addition to the epoxide group or by a urethane reaction using diisocyanates which are amine-blocked on one side with hydroxyl groups of an epoxy resin or by etherification reactions with corresponding phenol alkylation products. Crosslinking groupings which result in film formation at elevated temperature are also introduced into such resin systems.